/Engine/Source/Developer/DesktopPlatform/Public/IDesktopPlatform.h
Registers a directory as containing an engine installation
true if the directory was added. OutIdentifier will be set to the assigned identifier.
bool RegisterEngineInstallation ( const [FString](API\Runtime\Core\Containers\FString) & RootDir, [FString](API\Runtime\Core\Containers\FString) & OutIdentifier )